Hybrid propulsion systems

ABSTRACT

An example hybrid aircraft propulsion system includes one or more parallel propulsion units, each of the parallel propulsion units comprising: a first propulsor; a gas turbine engine configured to drive the first propulsor; and an electrical machine selectively configurable to: generate, for output via one or more electrical busses, electrical energy using mechanical energy derived from the first propulsor or the gas turbine engine; and drive the first propulsor using electrical energy received via the one or more electrical busses; and one or more series propulsion units, each of the series propulsion units comprising: a second propulsor; and an electrical machine selectively configurable to: generate, for output via the one or more electrical busses, electrical energy using mechanical energy derived from the second propulsor or the gas turbine engine; and drive the second propulsor using electrical energy received from one or more electrical busses.

TECHNICAL FIELD

This disclosure relates to hybrid propulsion systems.

BACKGROUND

A gas turbine engine is a type of internal combustion engine that may beused to power an aircraft, another moving vehicle, or an electricgenerator. The turbine in a gas turbine engine may be coupled to arotating compressor that increases a pressure of fluid flowing into theturbine. A combustor may add fuel to the compressed fluid and combustthe fuel/fluid combination. The combusted fluid may enter the turbine,where it expands, causing a shaft to rotate. The rotating shaft maydrive the compressor, a propulsor, other devices, and loads including anelectric generator. The propulsor may use the energy from the rotatingshaft to provide propulsion for the system.

SUMMARY

In general, this disclosure describes hybrid propulsion systems thatenable vehicles to be propelled using combinations of electrical motorsand combustion motors (e.g., thermodynamic engines such as gas turbineengines). As one example, in a series hybrid propulsion system, thecombustion motors may provide mechanical energy to operate one or moreelectrical generators, and the electrical motors may utilize powergenerated by the electrical generators to operate one or morepropulsors. As another example, in a parallel hybrid propulsion system,the combustion motors may provide mechanical energy to operate one ormore electrical generators and one or more propulsors, and theelectrical motors may utilize power generated by the electricalgenerators to operate the propulsors that are also operated by thecombustion motors. As another example, in a series-parallel hybridpropulsion system, the combustion motors may provide mechanical energyto operate one or more electrical generators and one or more propulsors,a first set of the electrical motors may utilize power generated by theelectrical generators to operate the propulsors that are also operatedby the combustion motors, and a second set of the electrical motors mayutilize power generated by the electrical generators to operate one ormore propulsors that are different than the propulsors operated by thecombustion motors.

In one example, an aircraft propulsion system includes: one or moreparallel propulsion units, each of the parallel propulsion unitscomprising: a propulsor of a first set of propulsors; a gas turbineengine configured to drive the propulsor; and an electrical machineselectively configurable to: generate, for output via one or moreelectrical busses, electrical energy using mechanical energy derivedfrom the propulsor or the gas turbine engine; and drive the propulsor ofthe first set of propulsors using electrical energy received via the oneor more electrical busses; and one or more series propulsion units, eachof the series propulsion units comprising: a propulsor of a second setof propulsors; and an electrical machine selectively configurable to:generate, for output via the one or more electrical busses, electricalenergy using mechanical energy derived from the propulsor or the gasturbine engine; and drive the propulsor of the second set of propulsorsusing electrical energy received from one or more electrical busses.

In another example, a method of propelling an aircraft includes driving,by one or more parallel propulsion units of the aircraft, one or morepropulsors of a first set of propulsors; outputting, by the one or moreparallel propulsion units of the aircraft, electrical energy onto one ormore electrical busses; and driving, by one or more series propulsionunits of the aircraft and using electrical energy received via the oneor more electrical busses, one or more propulsors of a second set ofpropulsors that is different than the first set of propulsors.

In another example, an airframe includes: one or more parallelpropulsion units, each of the parallel propulsion units comprising: apropulsor of a first set of propulsors; a gas turbine engine configuredto drive the propulsor; and an electrical machine selectivelyconfigurable to: generate, for output via one or more electrical busses,electrical energy using mechanical energy derived from the propulsor orthe gas turbine engine; and drive the propulsor of the first set ofpropulsors using electrical energy received via the one or moreelectrical busses; and one or more series propulsion units, each of theseries propulsion units comprising: a propulsor of a second set ofpropulsors; and an electrical machine selectively configurable to:generate, for output via the one or more electrical busses, electricalenergy using mechanical energy derived from the propulsor or the gasturbine engine; and drive the propulsor of the second set of propulsorsusing electrical energy received from one or more electrical busses.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual block diagram illustrating a system that includesa hybrid propulsion system, in accordance with one or more techniques ofthis disclosure.

FIG. 2 is a conceptual block diagram illustrating a system that includesa hybrid propulsion system in a series configuration, in accordance withone or more techniques of this disclosure.

FIG. 3 is a conceptual block diagram illustrating a system that includesa hybrid propulsion system in a series configuration with propulsiveenergy storage, in accordance with one or more techniques of thisdisclosure.

FIG. 4 is a conceptual block diagram illustrating a system that includesa hybrid propulsion system in a parallel configuration, in accordancewith one or more techniques of this disclosure.

FIG. 5 is a conceptual block diagram illustrating a system that includesa hybrid propulsion system in a series-parallel configuration, inaccordance with one or more techniques of this disclosure.

FIG. 6 is a conceptual block diagram illustrating a system that includesa hybrid propulsion system in a series-parallel configuration withpropulsive energy storage, in accordance with one or more techniques ofthis disclosure.

FIG. 7 is a conceptual diagram illustrating an example electrical layoutfor a hybrid propulsion system, in accordance with one or moretechniques of this disclosure.

FIG. 8 is a schematic diagram of an aircraft that includes a hybridpropulsion system, in accordance with one or more techniques of thisdisclosure.

DETAILED DESCRIPTION

Vehicles may include combustion motors that convert chemical potentialenergy (e.g., fuel) to propulsion and/or to electrical power. Inaddition to combustion motors, vehicles may include electrical machinesto create propulsion. A vehicle that includes both combustion motors andelectrical machines may be referred to as a hybrid vehicle. The motorsin hybrid vehicles may be configured as series, parallel, orseries-parallel.

In a series configuration, the combustion motor(s) may not directlyprovide power to propulsors, but instead may provide power in the formof rotational mechanical energy to one or more electric generators. Thegenerator(s) may provide electrical power to the electrical machine(s),which in turn provide power (i.e., rotational mechanical energy) to oneor more propulsors. In some examples, a vehicle with motors in a seriesconfiguration may include an energy storage system (ESS) capable ofstoring electrical energy for subsequent use by the electrical machines.The ESS may be charged with electrical energy generated by thegenerator(s) using mechanical energy from the combustion motor(s),electrical energy received from a source external to the vehicle (e.g.,ground power in the case of an aircraft), and/or electrical energygenerated by one or more other components of the vehicle. Some othercomponents of the vehicle that may generate electrical energy include,but are not limited to, the electrical machines (e.g., in a descentphase of flight in the case of an aircraft), solar panels, and the like.

In a parallel configuration, the combustion motor(s) and the electricalmachine(s) each may directly provide power to common propulsors. Forinstance, a combustion motor and an electrical machine may be configuredto provide power (i.e., rotational mechanical energy) to a commonpropulsor. The electrical machine may provide the power to the propulsorusing electrical power generated via the combustion motor (e.g., at atime when the electrical machine is not providing power to thepropulsor), electrical power received from an ESS, or electrical powergenerated by another combustion motor. In this way, the electric machinemay provide a “boost” of available power (e.g., for peak thrustoperations). Similar to the ESS in the series configuration, the ESS inthe parallel configuration may be charged with electrical energygenerated by the generator(s) using mechanical energy from thecombustion motor(s), electrical energy received from a source externalto the vehicle (e.g., ground power in the case of an aircraft), and/orelectrical energy generated by one or more other components of thevehicle.

In a series-parallel configuration, the combustion motor(s) and theelectrical machine(s) may directly provide power to propulsors. However,as opposed to the parallel configuration in which each propulsor ismechanically powered by at least a combustion motor, the series-parallelconfiguration includes at least one propulsor that is poweredexclusively by one or more electrical machines. That is, theseries-parallel configuration includes a first set of electricalmachines configured to provide power to a first set of propulsors thatare also directly powered by combustion motors and a second set ofelectrical machines configured to provide power to a second set ofpropulsors that are not directly powered by combustion motors. Similarto the ESS in the series and parallel configurations, the ESS in theseries-parallel configuration may be charged with electrical energygenerated by the generator(s) using mechanical energy from thecombustion motor(s), electrical energy received from a source externalto the vehicle (e.g., ground power in the case of an aircraft), and/orelectrical energy generated by one or more other components of thevehicle.

FIG. 1 is a conceptual block diagram illustrating a system 2 thatincludes a hybrid propulsion system, in accordance with one or moretechniques of this disclosure. As shown in FIG. 1, system 2 includes anelectrical bus 4, one or more power units 6A-6N (collectively, “powerunits 6”), one or more series propulsion modules 12A-12N (collectively,“series propulsion modules 12”), one or more non-hybrid propulsionmodules 18A-18N (collectively, “non-hybrid propulsion modules 18”), oneor more parallel propulsion modules 24A-24N (collectively, “parallelpropulsion modules 24”), an energy storage system (ESS) 34, and acontroller 36. System 2 may be included in, and provide propulsion to,any vehicle, such as an aircraft, a locomotive, or a watercraft. System2 may include additional components not shown in FIG. 1 or may notinclude some components shown in FIG. 1.

Electrical bus 4 provides electrical power interconnection betweenvarious components of system 2. Electrical bus 4 may include anycombination of one or more direct current (DC) bus, one or morealternating current (AC) electrical bus, or combinations thereof. As oneexample, electrical bus 4 may include a DC bus configured to transportelectrical power between power units 6 and series propulsion modules 12.As another example, electrical bus 4 may include plurality of redundantDC buses configured to transport electrical power between power units 6and series propulsion modules 12.

Power units 6 provide electrical power for use by various components ofsystem 2. As shown in FIG. 1, each of power units 6 includes one or morecombustion motors and one or more associated electrical machines. Forinstance, power unit 6A includes combustion motor 8A and electricalmachine 10A, and power unit 6N includes combustion motor 8N andelectrical machine 10N. In operation, combustion motor 8A utilizesconsumes fuel to produce rotational mechanical energy, which may beprovided to electric machine 10A via drive shaft 7A. Electric machine10A converts the rotational mechanical energy into electrical energy andoutputs the electrical energy to electrical bus 4. Each of thecombustion motors included in power units 6 may be any type ofcombustion motor. Examples of combustion motors include, but are notlimited to, reciprocating, rotary, and gas-turbines.

Each of power units 6 may have the same or different power generationcapacities. As one example, when operating at peak power, power unit 6Amay be capable of generating a greater amount of electrical power thanpower unit 6N. In this way, one or more of power units 6A-6N may beenabled, e.g., depending on a power demands of series propulsion modules12, other components of system 2, or both. As another example, whenoperating at peak power, power unit 6A and power unit 6N may be capableof generating the same amount of electrical power.

Series propulsion modules 12 convert electrical energy to propulsion. Asshown in FIG. 1, each of series propulsion modules 12 may include one ormore electrical machines and one or more propulsors. For instance,series propulsion module 12A includes electrical machine 14A andpropulsor 16A, and series propulsion module 12N includes electricalmachine 14N and propulsor 16N. In operation, series propulsion modules12 may operate in a plurality of modes including, but not limited to, anelectric-only mode, a regeneration mode, and a neutral mode.

When series propulsion module 12A operates in the electric-only mode,electrical machine 14A may consume electrical energy received viaelectrical bus 4 and convert the electrical energy to rotationalmechanical energy to power propulsor 16A. When series propulsion module12A operates in the regeneration mode, electrical machine 14A convertsrotational mechanical energy received from propulsor 16A into electricalenergy, and provides the electrical energy to electrical bus 4.Electrical bus 4 may distribute the electrical energy to another one ofseries propulsion modules 12, one of parallel propulsion modules 24, ESS34, or combinations thereof. When series propulsion module 12A operatesin the neutral mode, propulsor 16A may “windmill” and/or reduce itsfluid resistance (e.g., feather and/or blend with contours of anairframe).

Each of series propulsion modules 12 may have the same or differentpropulsion capacities. As one example, when operating at peak power,series propulsion module 12A may be capable of generating morepropulsive power than series propulsion module 12A. As another example,when operating at peak power, series propulsion module 12A may becapable of generating the same amount of propulsive power as seriespropulsion module 12A. As another example, series propulsion module 12Amay positioned at an outboard portion of a wing to provide greater yawcontrol while series propulsion module 12N may be positioned at aninboard portion of the wing in order to provide primary propulsion.

Non-hybrid propulsion modules 18 provide propulsion using fuel.Non-hybrid propulsion module 18 may be considered “non-hybrid” in thatnon-hybrid propulsion modules 18 neither generate electrical power foruse to generate propulsive force, nor consume electrical power toprovide propulsive force. As shown in FIG. 1, each of non-hybridpropulsion modules 18 may include one or more combustion motors and oneor more propulsors. For instance, non-hybrid propulsion module 18Aincludes combustion motor 20A and propulsor 22A, and non-hybridpropulsion module 18N includes combustion motor 20N and propulsor 22N.Non-hybrid propulsion modules 18 may operate in plurality of modesincluding, but not limited to, a combustion-only mode and a neutralmode. When non-hybrid propulsion module 18A operates in thecombustion-only mode, combustion motor 20A may consume fuel (e.g., froma fuel tank) to provide rotational mechanical energy to propulsor 22A.When non-hybrid propulsion module 18A operates in the neutral mode,propulsor 22A may “windmill” and/or reduce its resistance (e.g., featherand/or blend with contours of the airframe).

Each of non-hybrid propulsion modules 18 may have the same or differentpropulsion capacities. As one example, when operating at peak power,non-hybrid propulsion module 18A may be capable of generating apropulsive power than non-hybrid propulsion module 18N. As anotherexample, when operating at peak power, non-hybrid propulsion module 18Amay be capable of generating the same amount of propulsive power asnon-hybrid propulsion module 18N. As another example, non-hybridpropulsion module 18A may positioned at an outboard portion of a wing inorder to provide higher yaw control while non-hybrid propulsion module18N may be positioned at an inboard portion of the wing in order toprovide primary propulsion.

Parallel propulsion modules 24 provide propulsion using fuel andelectrical energy. As shown in FIG. 1, each of parallel propulsionmodules 24 may include one or more electric machines, one or morecombustion motors, and one or more propulsors. For instance, parallelpropulsion module 24A includes electric machine 26A, combustion motor30A, and propulsor 32A; and parallel propulsion module 24N includeselectric machine 26N, combustion motor 30N, and propulsor 32N. Parallelpropulsion modules 18 may operate in one or more of a plurality of modesincluding, but not limited to, a combustion-only mode, acombustion-generating mode, a dual-source mode, an electric-only mode, agenerating mode, a regenerating mode, and a neutral mode.

When parallel propulsion module 24A operates in the combustion-onlymode, combustion motor machine 30A may consume fuel (e.g., from a fueltank) to provide rotational mechanical energy to propulsor 32A whileelectric machine 26A may neither generate electrical power nor consumeelectrical power. When parallel propulsion module 24A operates in thecombustion-generating mode, combustion motor machine 30A may consumefuel (e.g., from a fuel tank) to provide rotational mechanical energy topropulsor 32A and electric machine 26A, and electric machine 26A mayconvert a portion of the rotational mechanical energy to electricalpower that is output to electrical bus 4. When parallel propulsionmodule 24A operates in the electric-only mode, combustion motor machine30A may be deactivated (e.g., not consume fuel) and electric machine 26Amay convert electrical power received from electrical bus 4 intorotational mechanical energy to power propulsor 32A. When parallelpropulsion module 24A operates in the dual-source mode, combustion motormachine 30A may consume fuel (e.g., from a fuel tank) to providerotational mechanical energy to propulsor 32A while electric machine 26Amay provide additional rotational mechanical energy to propulsor 32Ausing electrical energy sourced via electrical bus 4. When parallelpropulsion module 24A operates in the generating mode, combustion motormachine 30A may consume fuel (e.g., from a fuel tank) to providerotational mechanical energy to electric machine 26A, and electricmachine 26A may convert to rotational mechanical energy to electricalpower that is output to electrical bus 4. As compared to thecombustion-generating mode, when parallel propulsion module 24A operatesin the generating mode, propulsors 32 may be feathered or otherwisereduce or eliminate the amount of power taken from combustion motors 30(e.g., de-clutch from a drive shaft) such that a majority of the poweris used by electrical machines 26 to generate electrical power. Whenparallel propulsion module 24A operates in the regenerating mode,electric machine 26A may convert to rotational mechanical energyreceived from propulsor 32A to electrical power that is output toelectrical bus 4. When parallel propulsion module 24A operates in theneutral mode, propulsor 22A may “windmill” and/or reduce its fluidresistance (e.g., feather and/or blend with contours of the airframe).

Each of parallel propulsion modules 24 may have the same or differentpropulsion capacities. As one example, when operating at peak power,parallel propulsion module 24A may be capable of generating a propulsivepower than parallel propulsion module 24N. As another example, whenoperating at peak power, parallel propulsion module 24A may be capableof generating the same amount of propulsive power as parallel propulsionmodule 24N. As another example, parallel propulsion module 24A maypositioned at an outboard portion of a wing to provide higher yawcontrol while parallel propulsion module 24N may be positioned at aninboard portion of the wing in order to provide primary propulsion.

For modules that include electric machines and combustion motors (i.e.,power units 6 and parallel propulsion modules 24), the electric machinesmay be discrete components included in their own housing, or may beintegral to (i.e., included/embedded in) a same housing as thecombustion motors. As one example, electric machine 26A may be includedin same housing and/or directly mounted to combustion motor 30A. Asanother example, electric machine 26A may be attached to combustionmotor 30A via a drive shaft.

Additionally, for modules that include electric machines and combustionmotors, the modules may include an additional starter, be started bytheir respective electric machine(s), or be started through some othermeans. As one example, combustion motor 8A may include a starter that isdifferent than electric machine 10A. As another example, electricmachine 10A may operate as a starter for combustion motor 8A.

Energy storage system (ESS) 34 may provide energy storage capacity forsystem 2. ESS 34 may include any devices or systems capable of storingenergy (e.g., electrical energy). Examples of devices that may beincluded ESS 34 include, but are not limited to, batteries, capacitors,supercapacitors, flywheels, pneumatic storage, and any other devicecapable of storing electrical energy or energy that may be converted toelectrical energy (without combustion). ESS 34 may be coupled toelectrical bus 4 and may be capable of providing electrical energy toelectrical bus 4 and receiving electrical energy (e.g., for charging)from electrical bus 4.

In some examples, ESS 34 may include multiple energy storage systems.For instance, ESS 34 may include a first energy storage systemconfigured to store and provide electrical energy for propulsion and asecond energy storage system configured to store and provide electricalenergy for other systems, such as avionics and/or hotel loads. In someexamples, ESS 34 may include a single energy storage system. Forinstance, ESS 34 may include a single energy storage system configuredto store and provide electrical energy for propulsion and other systems.

In some examples, one or more components of ESS 34 may be swappable. Forexample, one or more batteries of ESS 34 may be swappable while anaircraft including system 2 is on the ground. As such, the aircraft maybe quickly able to return to a fully charged state without the need tocharge the batteries on the ground.

Controller 36 may control the operation of one or more components ofsystem 2. For instance, controller 36 may control the operation ofelectrical bus 4, power units 6, series propulsion modules 12,non-hybrid propulsion modules 18, parallel propulsion modules 24, andESS 34. In some examples, controller 36 may include a single controllerthat controls all of the components. In other examples, controller 36may include multiple controllers that each control one or morecomponents. Where controller 36 includes multiple controllers, thecontrollers may be arranged in any configuration. As one example,controller 36 may include a separate controller for each module type.For instance, controller 36 may include a first controller thatcontrollers power units 6, a second controller that controls seriespropulsion modules 12, a third controller that controls non-hybridpropulsion modules 18, and a fourth controller that controls parallelpropulsion modules 24. As another example, controller 36 may include aseparate controller for each module, or sub-module, within the moduletypes. For instance, controller 36 may include a separate controller foreach of power units 6, a separate controller for each of seriespropulsion modules 12, a separate controller for each of non-hybridpropulsion modules 18, and a separate controller for each of parallelpropulsion modules 24.

Controller 36 may comprise any suitable arrangement of hardware,software, firmware, or any combination thereof, to perform thetechniques attributed to controller 36 herein. Examples of controller 36include any one or more microprocessors, digital signal processors(DSPs), application specific integrated circuits (ASICs), fieldprogrammable gate arrays (FPGAs), or any other equivalent integrated ordiscrete logic circuitry, as well as any combinations of suchcomponents. When controller 36 includes software or firmware, controller36 further includes any necessary hardware for storing and executing thesoftware or firmware, such as one or more processors or processingunits.

In general, a processing unit may include one or more microprocessors,DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logiccircuitry, as well as any combinations of such components. Although notshown in FIG. 1, controller 36 may include a memory configured to storedata. The memory may include any volatile or non-volatile media, such asa random access memory (RAM), read only memory (ROM), non-volatile RAM(NVRAM), electrically erasable programmable ROM (EEPROM), flash memory,and the like. In some examples, the memory may be external to controller36 (e.g., may be external to a package in which controller 36 ishoused).

In operation, system 2 may include and be propelled by any combinationof series propulsion modules 12, non-hybrid propulsion modules 18, andparallel propulsion modules 24. As one example, in what may be referredto as a “series configuration,” system 2 may include one or more powerunits 6 and one or more series propulsion modules 12. Further details ofthe series configuration are discussed below with reference to FIG. 2.As another example, in what may be referred to as a “seriesconfiguration with propulsive energy storage,” system 2 may include oneor more power units 6, one or more series propulsion modules 12, and ESS34. Further details of the series configuration with propulsive energystorage are discussed below with reference to FIG. 3. As anotherexample, in what may be referred to as a “parallel configuration,”system 2 may include one or more parallel propulsion modules 24. Furtherdetails of the parallel configuration are discussed below with referenceto FIG. 4. As another example, in what may be referred to as a“series-parallel configuration,” system 2 may include one or more seriespropulsion modules 12 and one or more parallel propulsion modules 24.Further details of the series-parallel configuration are discussed belowwith reference to FIG. 5. As another example, in what may be referred toas a “series-parallel configuration with propulsive energy storage,”system 2 may include one or more series propulsion modules 12, one ormore parallel propulsion modules 24, and ESS 34. Further details of theseries-parallel configuration with propulsive energy storage arediscussed below with reference to FIG. 6.

Where multiple propulsion modules are present (e.g., multiple instancesof a specific type of propulsion module, multiple different types ofpropulsion modules, or combinations thereof), the multiple propulsionmodules may be controlled independently, collectively in groups, orcompletely collectively. As one example, in an example where system 2includes multiple series propulsion modules 12, each of seriespropulsion modules 12 may be independently controlled. As anotherexample, in an example where system 2 includes multiple seriespropulsion modules 12, all of series propulsion modules 12 may becollectively controlled. As another example, in an example where system2 includes multiple series propulsion modules 12, a first set of seriespropulsion modules 12 may be collectively controlled and a second set ofseries propulsion modules 12 may be collectively controlledindependently from the first set of series propulsion modules 12. Asanother example, in an example where system 2 includes multiple seriespropulsion modules 12 and multiple parallel propulsion modules 24, theseries propulsion modules 12 may be collectively controlled and theparallel propulsion modules 24 may be collectively controlledindependently from the series propulsion modules 12.

Any or all of the combustion motors described above (i.e., combustionmotors 8, combustion motors 20, and/or combustion motors 30) may, insome examples, be recuperated. That is, system 2 may include one or morerecuperators configured to improve the cycle efficiency of thecombustion motor(s). For instance, the recuperator may place an exhaustair flow that is downstream from a combustor in a combustion motor in aheat exchange relationship with a compressed airflow that is upstreamfrom the combustor such that the recuperator transfers thermal energyfrom the exhaust airflow to the compressed airflow.

FIG. 2 is a conceptual block diagram illustrating a system 2A thatincludes a hybrid propulsion system in a series configuration, inaccordance with one or more techniques of this disclosure. System 2A mayrepresent one example of system 2 of FIG. 1 that includes power unit 6A,series propulsion module 12A, and series propulsion module 12B. As shownin FIG. 2, system 2A also includes propulsion electrical bus 4A,critical electrical bus 4B, non-critical electrical bus 4C, controller35, controllers 37A-37D (collectively, “controllers 37”), AC/DCconverters 42A and 42B (collectively, “AC/DC converters 42”), and DC/ACconverters 44A and 44B (collectively, “DC/AC converters 44”).

Controller 35 and controllers 37 may collectively perform the functionsof controller 36 of FIG. 1. Controller 35 may operate as a system mastercontroller and controllers 37 may operate as sub-controllers. Forinstance, controller 37A may operate as an engine controller to controloperation of combustion motor 8A, controller 37B may operate as agenerator controller to control operation of electric machine 10A andAC/DC converters 42, controller 37C may operate as a propulsorcontroller to control operation of series propulsion modules 12 andDC/AC converters 44, and controller 37D may operate to control operationof ESS 34A. Any of controller 35 and controllers 37 may be combined intoone controller or further subdivided into additional controllers. As oneexample, controller 37A and controller 37B may be combined into a singlecontroller that controls operation of combustion motor 8A, electricmachine 10A and AC/DC converters 42. As another example, controller 37Cmay be subdivided into a first controller that controls DC/AC converter44A and series propulsion module 12A, and a second controller thatcontrols DC/AC converter 44B and series propulsion module 12B.

Controller 35 and controller 37 may be any type of controller capable ofcontrolling operation of the corresponding devices/modules. Forinstance, controller 37A may be an engine control unit (ECU) that may bepartial authority or full authority (i.e., controller 37A may be a fullauthority digital engine controller (FADEC)). Controller 35 andcontroller 37 may be implemented in any combination of hardware andsoftware.

As shown in the example of FIG. 2, electrical busses 4 of FIG. 1 may bedivided into propulsion electrical bus 4A, critical electrical bus 4B,and non-critical electrical bus 4C. Propulsion electrical bus 4A mayoperate to transport electrical power used for propulsion components ofsystem 2A. For instance, propulsion electrical bus 4A may facilitate thetransfer of electrical power between power unit 6A and series propulsionmodules 12. In the example FIG. 2, propulsion electrical bus 4A isimplemented as a DC bus or busses (e.g., a 700 volt DC bus). However, inother examples, propulsion electrical bus 4A may be implemented as an ACbus, AC busses, or a combination of one or more DC bus(es) and one ormore AC bus(es).

Critical electrical bus 4B may operate to transport electrical powerused by critical devices/systems of system 2A. Examples of criticaldevices/systems include, but are not limited to, engine controllers,avionics, flight control systems, and the like. Critical electrical bus4B may be implemented as any combination of one or more DC bus(es)and/or one or more AC bus(es). For instance, critical electrical bus 4Bmay be implemented as a 28 volt DC electrical bus.

Non-critical electrical bus 4C may operate to transport electrical powerused by non-critical devices/systems of system 2A. Examples ofnon-critical devices/systems include, but are not limited to, hotelloads 50, engine starters (e.g., a starter of combustion motor 8A), andthe like. Non-critical electrical bus 4C may be implemented as anycombination of one or more DC bus(es) and/or one or more AC bus(es). Forinstance, non-critical electrical bus 4C may be implemented as a 28 voltDC electrical bus.

Hotel loads 50 include devices and systems that consume electrical powerfor non-critical purposes (e.g., purposes other than propulsion andflight control). Examples of hotel loads 50 include, but are not limitedto, cabin lighting, cabin climate control, cooking, and the like.

AC/DC converters 42 may operate as rectifiers to convert AC electricalpower generated by one or more components of system 2A into DCelectrical power. For instance, AC/DC converters 42 may convert ACelectrical power generated by electric machine 10A into DC electricalpower that is output via propulsion electrical bus 4A.

DC/AC converters 44 may operate as inverters to convert DC electricalpower received from one or more components of system 2A into ACelectrical power. For instance, DC/AC converters 44 may convert DCelectrical power received via propulsion electrical bus 4A into ACelectrical power that is used by series propulsion modules 12 to providepropulsion to system 2A (e.g., used by electric machines 14A and 14B torespectively drive propulsors 16A and 16B).

As discussed above with reference to FIG. 1, in some examples, ESS 34may be capable of storing and providing electrical energy for propulsionand other systems/devices. In general, the size and/or weight of ESS 34may be dependent on the electrical storage capacity of ESS 34. Thegreater the electrical storage capacity, the greater the size and/orweight of ESS 34. The amount of electrical energy used for propulsionmay be significantly greater than the amount of electrical energy usedfor other systems/devices of system 2A. As such, the size and/or weightof ESS 34 in examples where ESS 34 is used to store electrical energyfor propulsion may be greater than the size and/or weight of ESS 34 inexamples where ESS 34 is not used to store electrical energy forpropulsion.

In accordance with one or more techniques of this disclosure, system 2Amay not include an energy storage system configured to store or provideelectrical energy for propulsion. For instance, as shown in FIG. 2, ESS34A may not be configured to output electrical energy to seriespropulsion modules 12 for driving propulsors 16. Similarly, in someexamples, ESS 34A may not be configured to receive electrical powergenerated by power unit 6A, which is configured to output electricalenergy to series propulsion modules 12 for driving propulsors 16. Assuch, by not using ESS 34A to store or provide electrical energy forpropulsion, the size and/or weight of ESS 34A may be reduced relative toenergy storage systems that are configured to store or provideelectrical energy for propulsion.

As discussed above, in some examples, ESS 34A may not be configured toreceive electrical power generated by power unit 6A. In some of suchexamples, ESS 34A may be charged while system 2A is on the ground and besized to have enough energy storage capacity to power systems/devicesattached to critical bus 4B and non-critical bus 4C for a projectedflight time. Additionally or alternatively, ESS 34A may be configured toreceive electrical energy generated by power unit 6A or any otherelectrical power source of system 2A (e.g., a different combustionoperated generator, solar panels, a ram-air turbine, or the like).

In operation, system 2A may function in a plurality of modes including,but not limited to, an electric-only mode and a neutral mode. In theelectric-only mode, controller 37A may cause combustion-motor 8A to burnfuel to generate rotational mechanical energy, which is used to driveelectric machine 10A via drive shaft 7A. Controller 37B may operateelectric machine 10A to convert the rotational mechanical energy into ACelectrical power, and operate AC/DC converters 42 to rectify the ACelectrical power into DC electrical power for output to propulsionelectrical bus 4A. Controller 37C may operate DC/AC converters 44 toconvert DC electrical power received from propulsion electrical bus 4Ainto AC electrical power for output to electrical machines 12.Controller 37C may operate electrical machines 12 to convert the ACelectrical power into rotational mechanical energy to drive a respectivepropulsor of propulsors 16.

In the neutral mode, controller 37A may shutdown combustion-motor 8Asuch that combustion-motor 8A ceases to burn fuel. Additionally, in someexamples, controller 37C may modify a shape/position/orientation of oneor more aspects of series propulsion modules 12 to reduce windresistance. As one example, where propulsors 16 include variable pitchpropellers, controller 37C may “feather” the blades of the propellers(i.e., rotate the blades to be substantially parallel with the airflow).As another example, controller 37C may fold-up all or portions ofpropulsors 16.

The hybrid system 2A may present one or more advantages. As one example,as discussed above, system 2A may reduce a weight of the energy storagesystem. As another example, system 2A may enable power to be imparted onthe DC bus from engine driven generators. As another example, system 2Amay allow propulsor motors to receive independent varying level of powerto enable the thrust differential between propulsors.

FIG. 3 is a conceptual block diagram illustrating a system 2B thatincludes a hybrid propulsion system in a series configuration withpropulsive energy storage, in accordance with one or more techniques ofthis disclosure. System 2B may include components similar to system 2Aof FIG. 2. However, as shown in FIG. 3, system 2B includes an energystorage system that is configured to store and provide electrical energyfor propulsion. For instance, system 2B includes ESS 34B, which iscoupled to propulsion electrical bus 4A and configured to providepropulsive electrical energy to series propulsion modules 12 viapropulsion electrical bus 4A. Additionally, ESS 34B may be configured toreceive electrical energy via propulsion electrical bus 4A.

In addition to the electric-only and neutral modes described above,system 2B may operate in a dual-source electric-only mode, aregenerating mode and a generating mode. In the dual-sourceelectric-only mode, controllers 37A and 37B may operate power unit 6Aand AC/DC converters 42 in a manner similar to the electric-only modediscussed above. Additionally, controller 37D may cause ESS 34B tooutput DC electrical power onto propulsion electrical bus 4A. Controller37C may operate DC/AC converters 44 and series propulsion modules 12 ina manner similar to the electric-only mode discusses above, with adifference being that electrical energy used by series propulsionmodules 12 for propulsion is contemporaneously sourced from power unit6A and ESS 34B.

In the regenerating mode, controller 37C may cause series propulsionmodules 12 to operate as generators (e.g., operate as ram air turbines)by converting rotational mechanical energy of propulsors 16 into ACelectrical power. Controllers 37C may operate DC/AC converters 44 toconvert the AC electrical power into DC electrical power for output topropulsion electrical bus 4A. Controller 37D may operate ESS 34B tocharge from propulsion electrical bus 4A using the DC electrical poweroutput by DC/AC converters 44.

In the generating mode, controllers 37A and 37B may operate power unit6A and AC/DC converters 42 in a manner similar to the electric-only modediscussed above. However, as opposed to controller 37C operating DC/ACconverters 44 and series propulsion modules 12 to utilize the generatedpower for propulsion, controller 37D may cause ESS 34B to store thegenerated power (i.e., to charge).

The hybrid system 2B may present one or more advantages. As one example,where the regenerating mode is used while an aircraft including system2B is descending, ESS 34B may obtain enough charge on decent to enablesystem 2B to operate in the dual-source electric-only mode on take-offand/or ascent without the need to charge ESS 34B on the ground.Additionally or alternatively, the generating mode may be used while theaircraft is on the ground such that ESS 34B may obtain enough charge toenable system 2B to operate in the dual-source electric-only mode ontake-off and/or ascent without the need to charge ESS 34B on the groundfrom an external charging source. As such, system 2B may enable hybridaircraft to utilize airports that lack ground charging facilities.

As another example, the dual-source electric mode may enable system 2Bto provide a similar amount of thrust with a relatively smaller sizedcombustion motor. As such, system 2B enables a weight reduction inhybrid aircraft. For similar reasons, system 2B may enable a reductionin emissions from aircraft.

As another example, system 2B may allow the transfer of excess power onthe DC bus to the ESS. For instance, ESS 34B may be “trickle” chargedusing excess power generated by power unit 6A (e.g., during cruise). Asanother example, system 2B may allow power to be imparted on the DC busfrom one or both of engine driven generators and ESS. The level of powerdemand placed on the DC bus is shared between ESS and engine drivengenerator system at varying percentage of power share depending on theoperational needs of the platform, available stored electrical energyand fuel. As another example, application of power from both the ESS andengine driven generator system in system 2B may allow the poweravailable on the bus to be higher than that from a standaloneturbo-generator offering a “boost” to the available power for peak powerdemand operations. As another example, application of power from boththe ESS and engine driven generator system in system 2B may allowfluctuating power demands on the bus to be met while maintaining aconstant power demand on the engine. As another example, system 2B mayallow propulsor motors to receive independent varying level of power toenable the thrust differential between propulsors. As another example,system 2B may allow the aircraft to self-start without the need to anexternal starter or APU. As another example, system 2B may deliver powerfor all hotel loads and avionics. As another example, system 2B maydeliver all power to all critical functions/systems.

While illustrated in FIGS. 2 and 3 as including a single power unit andmultiple series propulsion modules, systems 2A and 2B are not solimited. For instance, one or both of systems 2A and 2B may includemultiple power units and/or a single series propulsion module.

Including multiple power units may present one or more advantages. Asone example, a series hybrid system with multiple power units may bemore fault tolerant than a series hybrid system with a single powerunit. For instance, in a series hybrid system that includes two powerunits, flight power would still be available in the event that one ofthe power units failed or otherwise was shutdown.

FIG. 4 is a conceptual block diagram illustrating a system 2C thatincludes a hybrid propulsion system in a parallel configuration, inaccordance with one or more techniques of this disclosure. System 2C mayrepresent one example of system 2 of FIG. 1 that includes parallelpropulsion module 24A, and ESS 34B. As shown in FIG. 4, system 2C alsoincludes propulsion electrical bus 4A, critical electrical bus 4B, andnon-critical electrical bus 4C, controller 35, controllers 37, and AC/DCconverters 42.

Controllers 35 and 37 may perform operation similar to those discussedabove. For instance, controller 35 may operate as a system mastercontroller, controller 37A may control operation of combustion motor 30,controller 37B may control operation of electric machine 26A and AC/DCconverters 42, and controller 37D may control operation of ESS 34B.

However, as opposed to systems 2A and 2B that included series propulsionmodules (e.g., propulsion modules without a mechanical linkage betweencombustion motor and propulsor), system 2C includes parallel propulsionmodule 24A. While illustrated as including a single parallel propulsionmodule, system 2C is not so limited and may include a plurality ofparallel propulsion modules.

In operation, system 2C may function in a plurality of modes including,but not limited to, a combustion-only mode, a dual-source mode, acombustion-generating mode, an electric-only mode, a generating mode,and a regenerating mode. In the combustion-only mode, controller 37A maycause combustion-motor 30A to burn fuel to generate rotationalmechanical energy, which drives propulsor 32A. In the combustion-onlymode, electrical machine 26A may not supply or remove rotational energy(other than minimal frictional losses and the like) drive shaft 28A. Forinstance, electric machine 26A may be clutched or otherwise mechanicallydecoupled from drive shaft 28A.

In the dual-source mode, controller 37A may cause combustion-motor 30Ato burn fuel to generate rotational mechanical energy, which drivespropulsor 32A. Additionally, controller 37B may cause electric machine26A to add rotational energy to drive propulsor 32A using electricalenergy supplied from ESS 34B. In some examples, as opposed to causingdrive shaft 28A to rotate faster than the speed caused by combustionmotor 30A, electric machine 26A may provide additional torque to driveshaft 28A. As such, in examples where propulsor 32A is a variable pitchpropeller, controller 37A may adjust the pitch such that a higher levelof thrust is obtained without increasing the rotational speed topropulsor 32A.

In the combustion-generating mode, controller 37A may causecombustion-motor 30A to burn fuel to generate rotational mechanicalenergy, which drives propulsor 32A. Additionally, controller 37B maycause electric machine 26A to convert rotational energy generated bycombustion motor 30A into AC electrical power. Controller 37B may causeAC/DC converters to convert the AC electrical power into DC electricalpower for output onto propulsion electrical bus 4A. Controller 37D maycause ESS 34B to store the generated electrical power.

In the electric-only mode, controller 37A may cause combustion motor 30Ato shutdown and cease consuming fuel. Controller 37B may cause electricmachine 26A to convert electrical power sourced from ESS 34B intorotational mechanical energy to drive propulsor 32A.

In the generating mode, the components of system 2C may performfunctions similar to the combustion-generating mode with a differencebeing that controller 37A may cause propulsor 32A to decouple fromcombustion motor 30A or, if variable pitch, cause propulsor 32A tofeather. As such, controller 37A may cause all, or at least a vastmajority, of the rotational mechanical energy generated by combustionmotor 30A to be available for conversion into electrical energy byelectric machine 26A.

In the regenerating mode, the components of system 2C may performfunctions similar to the electric-only mode with a difference being thatthe flow of electrical power is reversed. For instance, parallelpropulsion module 24A may convert rotational mechanical energy receivedvia propulsor 32A into electrical energy that is stored by ESS 34B.

The parallel hybrid system 2C may present one or more advantages. As oneexample, the dual-source mode may enable system 2C to provide a similaramount of thrust with a relatively smaller sized combustion motor. Assuch, system 2C enables a weight reduction in hybrid aircraft. Forsimilar reasons, system 2B may enable a reduction in emissions fromaircraft.

As another example, as the combustion-generating mode enable system 2Cto store propulsion energy for future use (i.e., in ESS 34B), thecombustion-generating mode may enable controller 37A to operatecombustion motor 30A at an optimal level (e.g., a most fuel efficientlevel) without wasting energy, even if the energy resulting at theoptimal level is not immediately required. In other words, system 2C mayallow the transfer of excess power on the DC bus to the ESS for futureuse. As another example, application of mechanical power from electricmachine motoring may allow the power available on the propulsor shaft tobe higher than that from a standalone engine, thereby offering a “boost”to the available power for peak power thrust operations. As anotherexample, application of power from the ESS powered motor may allowfluctuating power demands on the shaft to be met while maintaining aconstant power demand on the engine. As another example, system 2C mayallow an aircraft to self-start without the need to an external starteror APU. As another example, system 2C may deliver power for all hotelloads and avionics. As another example, system 2C may deliver all powerto all critical functions/systems.

FIG. 5 is a conceptual block diagram illustrating a system 2D thatincludes a hybrid propulsion system in a series-parallel configuration,in accordance with one or more techniques of this disclosure. System 2Dmay include components similar to system 2A of FIG. 2 and system 2C ofFIG. 4. However, as shown in FIG. 5, the ESS 34 included in system 2D isnot configured to provide electrical energy for propulsion.

FIG. 6 is a conceptual block diagram illustrating a system 2E thatincludes a hybrid propulsion system in a series-parallel configurationwith propulsive energy storage, in accordance with one or moretechniques of this disclosure. System 2E may include components similarto system 2D of FIG. 5. However, as shown in FIG. 6, system 2E includesan energy storage system that is configured to store and provideelectrical energy for propulsion. For instance, system 2E includes ESS34B, which is coupled to propulsion electrical bus 4A and configured toprovide propulsive electrical energy to series propulsion modules 12and/or parallel propulsion module 24A via propulsion electrical bus 4A.Additionally, ESS 34B may be configured to receive electrical energy viapropulsion electrical bus 4A.

The series-parallel system 2E may be configured to operate in any of themodes described above with reference to the series and parallelconfigurations. Additionally, the series-parallel system 2E may operatein one or more additional modes. As one example, the series-parallelsystem 2E may operate in a dual source mode in which electrical energyused by series propulsion modules 12 is sourced from an energy storagesystem (e.g., ESS 34) and one or more power units (e.g., power units 6).In this dual source mode, the parallel propulsion modules (e.g.,parallel propulsion module 24A) may burn fuel to drive propulsors or maybe inactive. As another example, the series-parallel system 2E mayoperate in a triple source mode in which the parallel propulsion modules(e.g., parallel propulsion module 24A) may burn fuel to drive propulsors(e.g., propulsor 32A) and their electrical machines output electricalenergy via propulsion electrical bus 4A, electrical energy used byseries propulsion modules 12 is simultaneously sourced from all three ofan energy storage system (e.g., ESS 34), one or more power units (e.g.,power units 6), and the parallel propulsion modules.

The series-parallel hybrid system 2E may present one or more advantages.As one example, system 2E may allow power to be imparted on the DC busfrom one or both of engine driven generators and an ESS. As anotherexample, power demand level placed on the DC bus may be shared betweenESS and engine driven generator system at varying percentage of powershare depending on the operational needs of the platform, availablestored electrical energy and/or fuel. As another example, application ofmechanical power from electric machine motoring may allow the poweravailable on the propulsor shaft to be higher than that from astandalone engine, thereby offering a “boost” to the available power forpeak power thrust operations. As another example, application of powerfrom the ESS powered motor may allow fluctuating power demands on theshaft to be met while maintaining a constant power demand on the engine.As another example, application of power from both the ESS and enginedriven generator system may allow fluctuating power demands on the busto be met while maintaining a constant power demand on the engine. Asanother example, system 2E may allow propulsor motors to receiveindependent varying level of power to enable the thrust differentialbetween propulsors. As another example, system 2E may allow an aircraftto self-start without the need to an external starter or APU. As anotherexample, system 2E may deliver power for all hotel loads and avionics.As another example, system 2E may allow deliver all power to allcritical functions/systems.

FIG. 7 is a conceptual diagram illustrating an example electrical layoutfor a hybrid propulsion system, in accordance with one or moretechniques of this disclosure. As shown in FIG. 7, system 3 includespropulsion electrical bus 4A, critical electrical bus 4B, non-criticalelectrical bus 4C, series propulsion module 6A, parallel propulsionmodule 24A, AC/DC converters 42, DC/AC converters 44, controller 37A,critical power panel 62, propulsion power panel 60, ESS 34, ESS rack 64,ESS battery 66, engine starter 68, and external power interface 70.Propulsion electrical bus 4A, critical electrical bus 4B, non-criticalelectrical bus 4C, series propulsion module 6A, series propulsion module6A, parallel propulsion module 24A, AC/DC converters 42, DC/ACconverters 44, and controller 37A may perform operations describedabove.

As shown in FIG. 7, ESS 34 may include ESS rack 64, ESS battery 66, andexternal power interface 70. ESS rack 64 may operate to provideelectrical power to any of propulsion electrical bus 4A, criticalelectrical bus 4B, and non-critical electrical bus 4C. ESS rack 64 maybe coupled to each of the electrical busses 4A-4C, ESS battery 66, andexternal power interface 70. ESS rack 64 may facilitate the transfer ofelectrical power amongst various components. As one example, ESS rack 64may utilize electrical power stored in ESS battery 66 to supply 28 voltDC power to critical panel 62 via critical electrical bus 4B. As anotherexample, ESS rack 64 may utilize electrical power stored in ESS battery66 to supply 28 volt DC power to hotel loads 50 via non-criticalelectrical bus 4B. As another example, ESS rack 64 may utilizeelectrical power stored in ESS battery 66 to supply 700 volt DC power topropulsion power panel 60 via propulsion electrical bus 4A. As anotherexample, ESS rack 64 may utilize electrical power stored in ESS battery66 to supply 28 volt DC power to engine starter 68 to start a combustionengine.

External power interface 70 may enable system 3 to receive power fromone or more external sources and/or provide power to one or moreexternal loads. For instance, external power interface 70 may includeone or more electrical receptacles (e.g., plugs) that may be connectedto a terrestrial power grid at an airport to facilitate charging of ESSbattery 66.

As shown in FIG. 7, propulsion electrical bus 4A may include propulsionpower panel 60, which may facilitate the transfer of electrical powerbetween ESS 34, series propulsion module 6A, and parallel propulsionmodule 24A. Propulsion power panel 60 may include one or more mechanicalor solid state power switches to facilitate the power routing. In someexamples, propulsion power panel 60 may be capable of routing poweramongst any arbitrary combination of ESS 34, series propulsion module6A, and parallel propulsion module 24A. For instance, propulsion powerpanel 60 may include a full cross-point switching matrix.

As shown in FIG. 7, critical electrical bus 4B may include criticalpower panel 62, which may facilitate the transfer of electrical power tocritical systems/devices. In some examples, one or more additionalsystems/devices may be included in critical power panel 62. Forinstance, system master controller 72, which may be an example ofcontroller 35 or controller 36, may be included in critical power panel62.

Each of propulsion power panel 60, critical panel 62, and ESS rack 64may be discrete physical components. The physical components may belocated in a common area of an airframe, or at different areas aroundthe airframe. System 3 may include various electrical protectionselements in between and/or amongst power panel 60, critical panel 62,and ESS rack 64. For instance, system 3 may include components and beconfigured such that critical electrical bus 4B is functionally andphysically independent from other power systems (e.g., electrical busses4A and 4C).

FIG. 8 is a schematic diagram of an aircraft that includes a hybridpropulsion system, in accordance with one or more techniques of thisdisclosure. As shown in FIG. 8, aircraft 1000 include system 2F, whichincludes series propulsion modules 12A and 12B, ESS 34B, and power unit6A. In the example of FIG. 8, system 2F further includes recuperator 70and thermal management system (TMS) 80. As discussed above, recuperator70 may place an exhaust air flow that is downstream from a combustor(i.e., a combustor of combustion motor 8A) in a combustion motor in aheat exchange relationship with a compressed airflow that is upstreamfrom the combustor such that recuperator 70 transfers thermal energyfrom the exhaust airflow to the compressed airflow.

TMS 80 may be configured to manage thermal aspects of system 2F. Forinstance, TMS 80 may manage a temperature of a battery of ESS 34B. Insome examples TMS 80 may include one or more fans. In some examples, TMS80 may be fanless. As shown in FIG. 8, TMS 80 may include a heat ejector82 and a heat exchanger 84.

The following examples may illustrate one or more aspects of thedisclosure:

Example 1

A system comprising: one or more power units configured to outputelectrical energy onto one or more electrical busses; a plurality ofpropulsors; and a plurality of electrical machines, each respectiveelectrical machine configured to drive a respective propulsor of theplurality of propulsors using electrical energy received from at leastone of the one or more electrical busses.

Example 2

The system of example 1, further comprising one or more electricalenergy storage devices operably coupled to at least one of the one ormore electrical busses, wherein the electrical energy storage devicesare configured to both: charge using electrical energy sourced via theat least one of the one or more electrical busses; and discharge toprovide electrical energy to the at least one of the one or moreelectrical busses.

Example 3

The system of example 2, wherein pairs of the propulsors and theelectrical machines each comprise respective series propulsion units,the system further comprising: one or more parallel propulsion units.

Example 4

The system of example 1, wherein the system does not include an energystorage system configured to provide electrical energy to the pluralityof electrical machines for driving the propulsors.

Example 5

The system of example 4, further comprising one or more electricalenergy storage devices configured to provide electrical energy to one ormore devices other than the plurality of electrical machines.

Example 6

The system of any combination of examples 1-5, wherein at least one ofthe plurality of electrical machines is configured to: generateelectrical energy using mechanical energy derived from a correspondingpropulsor; and output the generated electrical energy onto the one ormore electrical busses.

Example 7

The system of any combination of examples 1-6, wherein the one or moreelectrical busses comprise direct current (DC) electrical busses.

Example 8

The system of any combination of examples 1-7, wherein the one or morepower units comprise a plurality of power units.

Example 9

The system of example 8, wherein an amount of electrical energygenerated by each of the plurality of power units is independentlycontrollable.

Example 10

A method of propelling an aircraft, the method comprising: outputting,by one or more power units, electrical energy onto one or moreelectrical busses; and driving, by each respective electrical machine ofa plurality of electrical machines and using electrical energy receivedfrom at least one of the electrical busses, a respective propulsor of aplurality of propulsors.

Example 11

The method of example 10, further comprising: charging, by one or moreelectrical energy storage systems, using electrical energy sourced viathe at least one or more electrical busses; and discharging, by the oneor more electrical energy storage systems, to provide electrical energyto the at least one of the one or more electrical busses.

Example 12

The method of example 11, wherein the discharging to provide electricalenergy to the one or more electrical busses, the outputting electricalenergy to the one or more electrical busses, and the driving thepropulsors using electrical energy received from the electrical bussesare performed simultaneously in a dual source mode.

Example 13

The method of any combination of examples 10-12, wherein the one or morepower units comprise at least a first power unit and a second powerunit, and wherein outputting the electrical energy comprises:outputting, at a first time and by the first power unit, a first amountof electrical energy via the one or more electrical busses; andoutputting, at the first time and by the second power unit, the firstamount of electrical energy via the one or more electrical busses.

Example 14

The method of example 13, wherein outputting the electrical energycomprises: outputting, at a second time and by the first power unit, asecond amount of electrical energy via the one or more electricalbusses; and outputting, at the second time and by the second power unit,a third amount of electrical energy via the one or more electricalbusses, wherein the third amount of electrical energy is different thanthe second amount of electrical energy.

Example 15

The method of any combination of examples 10-14, wherein pairs of thepropulsors and the electrical machines each comprise respective seriespropulsion units, the method further comprising: driving, by one or morecombustion motors that are not included in the series propulsion units,one or more propulsors that are not included in the series propulsionunits.

Example 16

An airframe comprising: one or more power units configured to outputelectrical energy onto one or more electrical busses; a plurality ofpropulsors; and a plurality of electrical machines, each respectiveelectrical machine configured to drive a respective propulsor of theplurality of propulsors using electrical energy received from at leastone of the one or more electrical busses.

Example 17

The airframe of example 16, further comprising one or more electricalenergy storage devices operably coupled to at least one of the one ormore electrical busses, wherein the electrical energy storage devicesare configured to both: charge using electrical energy sourced via theat least one of the one or more electrical busses; and discharge toprovide electrical energy to the at least one of the one or moreelectrical busses.

Example 18

The airframe of example 17, wherein pairs of the propulsors and theelectrical machines each comprise respective series propulsion units,the airframe further comprising: one or more parallel propulsion units.

Example 19

The airframe of example 16, wherein the airframe does not include anelectrical energy storage system configured to provide electrical energyto the plurality of electrical machines for driving the propulsors.

Example 20

The airframe of any combination of examples 16-19, wherein the one ormore power units comprise a plurality of power units.

Example 21

A system comprising: a plurality of power units configured to outputelectrical energy onto one or more electrical busses; one or morepropulsors; and one or more electrical machines, each respectiveelectrical machine configured to drive a respective propulsor of the oneor more propulsors using electrical energy received from at least one ofthe one or more electrical busses.

Example 22

The system of example 21, further comprising one or more electricalenergy storage devices operably coupled to at least one of the one ormore electrical busses, wherein the electrical energy storage devicesare configured to both: charge using electrical energy sourced via theat least one of the one or more electrical busses; and discharge toprovide electrical energy to the at least one of the one or moreelectrical busses.

Example 23

The system of example 22, wherein pairs of the propulsors and theelectrical machines each comprise respective series propulsion units,the system further comprising: one or more parallel propulsion units.

Example 24

The system of example 21, wherein the system does not include an energystorage system configured to provide electrical energy to the pluralityof electrical machines for driving the propulsors.

Example 25

The system of example 24, further comprising one or more electricalenergy storage devices configured to provide electrical energy to one ormore devices other than the plurality of electrical machines.

Example 26

The system of any combination of examples 21-25, wherein at least one ofthe plurality of electrical machines is configured to: generateelectrical energy using mechanical energy derived from a correspondingpropulsor; and output the generated electrical energy onto the one ormore electrical busses.

Example 27

The system of any combination of examples 21-26, wherein the one or moreelectrical busses comprise direct current (DC) electrical busses.

Example 28

The system of any combination of examples 21-27, wherein the one or moreelectrical machines comprise a plurality of electrical machines, andwherein the one or more propulsors comprise a plurality of propulsors.

Example 29

The system of any combination of examples 21-28, wherein an amount ofelectrical energy generated by each of the plurality of power units isindependently controllable.

Example 30

A method of propelling an aircraft, the method comprising: outputting,by a plurality of power units, electrical energy onto one or moreelectrical busses; and driving, by one or more electrical machines andusing electrical energy received from at least one of the electricalbusses, one or more propulsors.

Example 31

The method of example 30, further comprising: charging, by one or moreelectrical energy storage systems, using electrical energy sourced viathe at least one or more electrical busses; and discharging, by the oneor more electrical energy storage systems, to provide electrical energyto the at least one of the one or more electrical busses.

Example 32

The method of example 31, wherein the discharging to provide electricalenergy to the one or more electrical busses, the outputting electricalenergy to the one or more electrical busses, and the driving the one ormore propulsors using electrical energy received from the electricalbusses are performed simultaneously in a dual source mode.

Example 33

The method of any combination of examples 30-32, wherein the pluralityof power units comprises at least a first power unit and a second powerunit, and wherein outputting the electrical energy comprises:outputting, at a first time and by the first power unit, a first amountof electrical energy via the one or more electrical busses; andoutputting, at the first time and by the second power unit, the firstamount of electrical energy via the one or more electrical busses.

Example 34

The method of any combination of examples 30-33, wherein outputting theelectrical energy comprises: outputting, at a second time that isdifferent than the first time and by the first power unit, a secondamount of electrical energy via the one or more electrical busses; andoutputting, at the second time and by the second power unit, a thirdamount of electrical energy via the one or more electrical busses,wherein the third amount of electrical energy is different than thesecond amount of electrical energy.

Example 35

The method of any combination of examples 30-34, wherein pairs of thepropulsors and the electrical machines each comprise respective seriespropulsion units, the method further comprising: driving, by one or morecombustion motors that are not included in the series propulsion units,one or more propulsors that are not included in the series propulsionunits.

Example 36

An airframe comprising: a plurality of power units configured to outputelectrical energy onto one or more electrical busses; one or morepropulsors; and one or more electrical machines, each respectiveelectrical machine configured to drive a respective propulsor of the oneor more propulsors using electrical energy received from at least one ofthe one or more electrical busses.

Example 37

The airframe of example 36, further comprising one or more electricalenergy storage devices operably coupled to at least one of the one ormore electrical busses, wherein the electrical energy storage devicesare configured to both: charge using electrical energy sourced via theat least one of the one or more electrical busses; and discharge toprovide electrical energy to the at least one of the one or moreelectrical busses.

Example 38

The airframe of example 37, wherein pairs of the propulsors and theelectrical machines each comprise respective series propulsion units,the airframe further comprising: one or more parallel propulsion units.

Example 39

The airframe of example 36, wherein the airframe does not include anelectrical energy storage system configured to provide electrical energyto the plurality of electrical machines for driving the propulsors.

Example 40

The airframe of any combination of examples 36-39, wherein the one ormore power units comprise a plurality of power units.

Example 41

An aircraft propulsion system comprising: one or more parallelpropulsion units, each of the parallel propulsion units comprising: apropulsor of a first set of propulsors; a gas turbine engine configuredto drive the propulsor; and an electrical machine selectivelyconfigurable to: generate, for output via one or more electrical busses,electrical energy using mechanical energy derived from the propulsor orthe gas turbine engine; and drive the propulsor of the first set ofpropulsors using electrical energy received via the one or moreelectrical busses; and one or more series propulsion units, each of theseries propulsion units comprising: a propulsor of a second set ofpropulsors; and an electrical machine selectively configurable to:generate, for output via the one or more electrical busses, electricalenergy using mechanical energy derived from the propulsor or the gasturbine engine; and drive the propulsor of the second set of propulsorsusing electrical energy received from one or more electrical busses.

Example 42

The system of example 41, further comprising one or more electricalenergy storage devices operably coupled to at least one of the one ormore electrical busses, wherein the electrical energy storage devicesare configured to both: charge using electrical energy sourced via theat least one of the one or more electrical busses; and discharge toprovide electrical energy to the at least one of the one or moreelectrical busses.

Example 43

The system of any combination of examples 40-42, further comprising: oneor more power units configured to generate and output electrical energyvia at least one of the one or more electrical busses.

Example 44

The system of any combination of examples 40-43, wherein each of thepower units, the parallel propulsion units, and the series propulsionunits are independently controllable.

Example 45

The system of any combination of examples 40-44, wherein the one or moreparallel propulsion units includes only a single parallel propulsionunit and the one or more series propulsion units include a plurality ofseries propulsion units.

Example 46

The system of example 45, wherein the single parallel propulsion unit ispositioned on a centerline of the aircraft, and wherein the plurality ofseries propulsion units are positionally mirrored across the centerlineof the aircraft.

Example 47

A method of propelling an aircraft, the method comprising: driving, byone or more parallel propulsion units of the aircraft, one or morepropulsors of a first set of propulsors; outputting, by the one or moreparallel propulsion units of the aircraft, electrical energy onto one ormore electrical busses; and driving, by one or more series propulsionunits of the aircraft and using electrical energy received via the oneor more electrical busses, one or more propulsors of a second set ofpropulsors that is different than the first set of propulsors.

Example 48

The method of example 47, further comprising: outputting, by one or morepower units, electrical energy onto the one or more electrical busses.

Example 49

The method of example 48, further comprising: operating the aircraft ina dual source mode by at least simultaneously driving the one or morepropulsors of the first set of propulsors, outputting electrical energyby the one or more power units, and driving the one or more propulsorsof the second set of propulsors.

Example 50

The method of example 49, further comprising: charging, by an electricalstorage system of the aircraft, using electrical energy sourced via theat least one of the one or more electrical busses; and discharging, bythe electrical storage system, to provide electrical energy to the atleast one of the one or more electrical busses.

Example 51

The method of example 50, further comprising: operating the aircraft ina triple source mode by at least simultaneously driving the one or morepropulsors of the first set of propulsors, outputting electrical energyby the one or more power units, discharging the electrical storagesystem, and driving the one or more propulsors of the second set ofpropulsors.

Example 52

The method of any combination of examples 47-51, further comprising:operating the aircraft in an electric-only mode by at leastsimultaneously driving the one or more propulsors of the first set ofpropulsors, driving the one or more propulsors of the second set ofpropulsors, and causing the parallel propulsion units to refrain fromburning fuel.

Example 53

An aircraft propulsion system comprising: one or more parallelpropulsion units, each of the parallel propulsion units comprising: apropulsor of a first set of propulsors; a gas turbine engine configuredto drive the propulsor; and an electrical machine selectivelyconfigurable to: generate, for output via one or more electrical busses,electrical energy using mechanical energy derived from the propulsor orthe gas turbine engine; and drive the propulsor of the first set ofpropulsors using electrical energy received via the one or moreelectrical busses; and one or more series propulsion units, each of theseries propulsion units comprising: a propulsor of a second set ofpropulsors; and an electrical machine selectively configurable to:generate, for output via the one or more electrical busses, electricalenergy using mechanical energy derived from the propulsor or the gasturbine engine; and drive the propulsor of the second set of propulsorsusing electrical energy received from one or more electrical busses.

Example 54

The system of example 53, further comprising one or more electricalenergy storage devices operably coupled to at least one of the one ormore electrical busses, wherein the electrical energy storage devicesare configured to both: charge using electrical energy sourced via theat least one of the one or more electrical busses; and discharge toprovide electrical energy to the at least one of the one or moreelectrical busses.

Example 55

The system of any combination of examples 53-54, further comprising: oneor more power units configured to generate and output electrical energyvia at least one of the one or more electrical busses.

Example 56

The system of any combination of examples 53-55, further comprising: oneor more controllers configured to operate the aircraft in a dual sourcemode by at least simultaneously causing the parallel propulsion units todrive the first set of propulsors using fuel, causing the power units tooutput electrical energy via the one or more electrical busses, causingthe electrical storage system to discharge to output electrical energyvia the one or more electrical busses, and causing the series propulsionunits to drive the second set of propulsors using electrical energyreceived via the one or more electrical busses.

Example 57

The system of any combination of examples 53-56, further comprising: oneor more controllers configured to operate the aircraft in a dual sourceelectric-only mode by at least simultaneously causing the parallelpropulsion units to drive the first set of propulsors using electricalenergy received via the one or more electrical busses without the gasturbine engines using fuel, causing the power units to output electricalenergy via the one or more electrical busses, causing the electricalstorage system to discharge to output electrical energy via the one ormore electrical busses, and causing the series propulsion units to drivethe second set of propulsors using electrical energy received via theone or more electrical busses.

Example 58

The system of any combination of examples 53-57, wherein each of thepower units, the parallel propulsion units, and the series propulsionunits are independently controllable.

Example 59

The system of any combination of examples 53-58, wherein the one or moreparallel propulsion units includes only a single parallel propulsionunit and the one or more series propulsion units include a plurality ofseries propulsion units.

Example 60

The system of example 59, wherein the single parallel propulsion unit ispositioned on a centerline of the aircraft, and wherein the plurality ofseries propulsion units are positionally mirrored across the centerlineof the aircraft.

Example 61

An aircraft propulsion system comprising: a plurality of electricalbusses comprising a propulsion bus, a critical bus, and a non-criticalbus; an electrical energy storage system coupled to each of theplurality of electrical busses; one or more power units configured togenerate and output electrical energy via the propulsion bus; one ormore electrical machines configured to drive respective propulsors usingelectrical energy received via the propulsion bus; one or more hotelloads configured to receive energy via the non-critical bus; and one ormore critical loads configured to receive energy via the critical bus.

Example 62

The system of example 61, wherein at least one of the electricalmachines is included in a parallel propulsion module.

Example 63

The system of any combination of examples 61-62, wherein at least one ofthe electrical machines is included in a series propulsion module.

Example 64

The system of any combination of examples 61-63, wherein the electricalenergy storage system includes an interface for receiving electricalenergy from an electrical energy source external to the aircraft.

Example 65

The system of example 64, wherein the interface is further configured toprovide electrical energy to a load external to the aircraft.

Example 66

The system of any combination of examples 61-65, wherein the propulsionbus comprises a relatively high voltage direct current (DC) bus, and thecritical and non-critical busses comprise relatively low voltage DCbusses.

Example 67

The system of any combination of examples 61-66, wherein the propulsionbus includes a propulsion power panel.

Example 68

A method comprising: outputting, by one or more power units, electricalenergy via a propulsion electrical bus; driving, by one or moreelectrical machines, respective propulsors using electrical energyreceived via the propulsion electrical bus; outputting, by an electricalenergy storage system, electrical energy via a non-critical electricalbus and a critical electrical bus; receiving, by one or more hotelloads, electrical energy via the non-critical electrical bus; andreceiving, by one or more critical loads, electrical energy via thecritical electrical bus.

Example 69

The method of example 68, further comprising: outputting, by theelectrical energy storage system, electrical energy via the propulsionelectrical bus.

Example 70

The method of example 69, further comprising: charging, by theelectrical energy storage system, using electrical energy received viathe propulsion electrical bus.

Example 71

The method of any combination of examples 68-70, further comprising:outputting, by one or more parallel propulsion units, electrical energyvia the propulsion electrical bus.

Example 72

The method of example 71, wherein driving the propulsors comprises:driving, by electrical machines included in the parallel propulsionunits, propulsors of the parallel propulsion units using electricalenergy received via the propulsion electrical bus.

Example 73

An airframe comprising: a plurality of electrical busses comprising apropulsion bus, a critical bus, and a non-critical bus; an electricalenergy storage system coupled to each of the plurality of electricalbusses; one or more power units configured to generate and outputelectrical energy via the propulsion bus; one or more electricalmachines configured to drive respective propulsors using electricalenergy received via the propulsion bus; one or more hotel loadsconfigured to receive energy via the non-critical bus; and one or morecritical loads configured to receive energy via the critical bus.

Example 74

The airframe of example 73, wherein at least one of the electricalmachines is included in a parallel propulsion module.

Example 75

The airframe of any combination of examples 73-74, wherein at least oneof the electrical machines is included in a series propulsion module.

Example 76

The airframe of any combination of examples 73-75, wherein theelectrical energy storage system includes an interface for receivingelectrical energy from an electrical energy source external to theairframe.

Example 77

The airframe of any combination of examples 73-76, wherein the interfaceis further configured to provide electrical energy to a load external tothe airframe.

Example 78

The airframe of any combination of examples 73-77, wherein thepropulsion bus comprises a relatively high voltage direct current (DC)bus, and the critical and non-critical busses comprise relatively lowvoltage DC busses.

Example 79

The airframe of any combination of examples 73-78, wherein thepropulsion bus comprises a plurality of redundant propulsion busses.

Example 80

The airframe of any combination of examples 73-79, further comprising: arecuperator for at least one of the power units.

Example 81

A system or airframe comprising any combination of examples 1-9, 16-20,21-29, 36-40, 41-46, 53-60, 61-67, and 73-80.

Example 82

A method comprising any combination of examples 10-15, 30-35, 47-52, and68-72.

Example 83

A computer-readable storage medium storing instructions that, whenexecuted, cause one or more controllers to perform the method of anycombination of examples 10-15, 30-35, 47-52, and 68-72.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. An aircraft propulsion system comprising: one ormore parallel propulsion units, each of the parallel propulsion unitscomprising: a propulsor of a first set of propulsors; a gas turbineengine configured to drive the propulsor; and an electrical machineselectively configurable to: generate, for output via one or moreelectrical busses, electrical energy using mechanical energy derivedfrom the propulsor or the gas turbine engine; and drive the propulsor ofthe first set of propulsors using electrical energy received via the oneor more electrical busses; and one or more series propulsion units, eachof the series propulsion units comprising: a propulsor of a second setof propulsors; and an electrical machine selectively configurable to:generate, for output via the one or more electrical busses, electricalenergy using mechanical energy derived from the propulsor or the gasturbine engine; and drive the propulsor of the second set of propulsorsusing electrical energy received from one or more electrical busses. 2.The system of claim 1, further comprising one or more electrical energystorage devices operably coupled to at least one of the one or moreelectrical busses, wherein the electrical energy storage devices areconfigured to both: charge using electrical energy sourced via the atleast one of the one or more electrical busses; and discharge to provideelectrical energy to the at least one of the one or more electricalbusses.
 3. The system of claim 1, further comprising: one or more powerunits configured to generate and output electrical energy via at leastone of the one or more electrical busses.
 4. The system of claim 3,wherein each of the power units, the parallel propulsion units, and theseries propulsion units are independently controllable.
 5. The system ofclaim 1, wherein the one or more parallel propulsion units includes onlya single parallel propulsion unit and the one or more series propulsionunits include a plurality of series propulsion units.
 6. The system ofclaim 5, wherein the single parallel propulsion unit is positioned on acenterline of the aircraft, and wherein the plurality of seriespropulsion units are positionally mirrored across the centerline of theaircraft.
 7. A method of propelling an aircraft, the method comprising:driving, by one or more parallel propulsion units of the aircraft, oneor more propulsors of a first set of propulsors; outputting, by the oneor more parallel propulsion units of the aircraft, electrical energyonto one or more electrical busses; and driving, by one or more seriespropulsion units of the aircraft and using electrical energy receivedvia the one or more electrical busses, one or more propulsors of asecond set of propulsors that is different than the first set ofpropulsors.
 8. The method of claim 7, further comprising: outputting, byone or more power units, electrical energy onto the one or moreelectrical busses.
 9. The method of claim 8, further comprising:operating the aircraft in a dual source mode by at least simultaneouslydriving the one or more propulsors of the first set of propulsors,outputting electrical energy by the one or more power units, and drivingthe one or more propulsors of the second set of propulsors.
 10. Themethod of claim 9, further comprising: charging, by an electricalstorage system of the aircraft, using electrical energy sourced via theat least one of the one or more electrical busses; and discharging, bythe electrical storage system, to provide electrical energy to the atleast one of the one or more electrical busses.
 11. The method of claim10, further comprising: operating the aircraft in a triple source modeby at least simultaneously driving the one or more propulsors of thefirst set of propulsors, outputting electrical energy by the one or morepower units, discharging the electrical storage system, and driving theone or more propulsors of the second set of propulsors.
 12. The methodof claim 10, further comprising: operating the aircraft in anelectric-only mode by at least simultaneously driving the one or morepropulsors of the first set of propulsors, driving the one or morepropulsors of the second set of propulsors, and causing the parallelpropulsion units to refrain from burning fuel.
 13. An aircraftpropulsion system comprising: one or more parallel propulsion units,each of the parallel propulsion units comprising: a propulsor of a firstset of propulsors; a gas turbine engine configured to drive thepropulsor; and an electrical machine selectively configurable to:generate, for output via one or more electrical busses, electricalenergy using mechanical energy derived from the propulsor or the gasturbine engine; and drive the propulsor of the first set of propulsorsusing electrical energy received via the one or more electrical busses;and one or more series propulsion units, each of the series propulsionunits comprising: a propulsor of a second set of propulsors; and anelectrical machine selectively configurable to: generate, for output viathe one or more electrical busses, electrical energy using mechanicalenergy derived from the propulsor or the gas turbine engine; and drivethe propulsor of the second set of propulsors using electrical energyreceived from one or more electrical busses.
 14. The system of claim 13,further comprising one or more electrical energy storage devicesoperably coupled to at least one of the one or more electrical busses,wherein the electrical energy storage devices are configured to both:charge using electrical energy sourced via the at least one of the oneor more electrical busses; and discharge to provide electrical energy tothe at least one of the one or more electrical busses.
 15. The system ofclaim 13, further comprising: one or more power units configured togenerate and output electrical energy via at least one of the one ormore electrical busses.
 16. The system of claim 15, further comprising:one or more controllers configured to operate the aircraft in a dualsource mode by at least simultaneously causing the parallel propulsionunits to drive the first set of propulsors using fuel, causing the powerunits to output electrical energy via the one or more electrical busses,causing the electrical storage system to discharge to output electricalenergy via the one or more electrical busses, and causing the seriespropulsion units to drive the second set of propulsors using electricalenergy received via the one or more electrical busses.
 17. The system ofclaim 15, further comprising: one or more controllers configured tooperate the aircraft in a dual source electric-only mode by at leastsimultaneously causing the parallel propulsion units to drive the firstset of propulsors using electrical energy received via the one or moreelectrical busses without the gas turbine engines using fuel, causingthe power units to output electrical energy via the one or moreelectrical busses, causing the electrical storage system to discharge tooutput electrical energy via the one or more electrical busses, andcausing the series propulsion units to drive the second set ofpropulsors using electrical energy received via the one or moreelectrical busses.
 18. The system of claim 15, wherein each of the powerunits, the parallel propulsion units, and the series propulsion unitsare independently controllable.
 19. The system of claim 13, wherein theone or more parallel propulsion units includes only a single parallelpropulsion unit and the one or more series propulsion units include aplurality of series propulsion units.
 20. The system of claim 19,wherein the single parallel propulsion unit is positioned on acenterline of the aircraft, and wherein the plurality of seriespropulsion units are positionally mirrored across the centerline of theaircraft.